customization of fallback-mode is not possible unless you edit the code
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gnome-tweak-tool for fonts.
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for colors, you will need to create a GTK theme of your own
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metacity is used in the fallback mode in fallback mode you can use gconf-editor to switch your metacity theme as before
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metacity (and mutter) will probably be ported to gsettings (dconf is a gsettings backend) for gnome 3.2
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gnome-tweak-tool's source code is Python and really easy to follow, so if there's any setting you want to easily toggle that's not there yet, just add it :)
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gnome 3.2 will be in F16 the goal is to get rid of gconf
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GNOME 3.0 final is just about to land, and Fedora 15 is out in just over a month :) no time for 3.2"